Denitrogenation of hydrocarbon mixtures



United States Patent This invention relates to the purification of contaminated hydrocarbon mixtures and particularly to the removal of nitrogen compounds from such mixtures. This invention specifically relates to the dentitrogenation of higher boiling hydrocarbon mixtures which are subsequently hydrocracked to a lower boiling hydrocarbon product.

Many naturally occurring hydrocarbon mixtures such as petroleum streams are found to contain considerable quantities of hydrocarbon derivatives of nitrogen in addition to the principal hydrocarbon constituents. The presence of nitrogen-containing impurities in hydrocarbon mixtures causes offensive odors and their presence adversely affects hydrocarbon refining techniques by which fuels, solvents, and other materials are produced. Nitrogen compounds have, for example, well defined adverse effects on such processes as catalytic cracking, catalytic isomerization, and catalytic reforming. Nitrogen compounds appear to react with the catalyst or promoter forming ammonium compounds which deposit solids in the reaction zone with the result that catalysts are deactivated and destroyed, and yields are lowered.

In the past it has been common practice to treat hydrocarbon feed stocks for desulfurization. It is manifest to those skilled in the art that a decontaminating unit which produces a satisfactorily desulfurized charge stock will not necessarily produce a charge stock having a satisfactory nitrogen content. Furthermore, processing stocks with high nitrogen content requires a much higher severity to convert nitrogen contaminants to a form in which they are not harmful to the catalyst.

Because of the adverse effects of nitrogen compounds upon cracking catalysts and because of high severities required to treat feed stocks with high nitrogen contents, repeated attempts have been made to remove nitrogen compounds from hydrocarbon feed stocks for refining processes.

However, prior art processes have several disadvantages. For example, one method disclosed in the prior art for denitrogenation of contaminated hydrocarbon mixtures uses a multiple staged system. Feed stocks are first treated with a nitrogen-insensitive catalyst. This treatment lowers nitrogen compound concentration, but subsequent contact with a nitrogen-sensitive catalyst is necessary to reduce nitrogen concentration to a satisfactory level. Such a process has been found effective for hydrocarbon mixtures contaminated with nitrogen compounds in a low concentrations on the order of parts per million. Feed stocks with higher nitrogen concentrations cannot be treated in such a process without dilution.

It has now been found according to the present invention that hydrocarbon mixtures originally contaminated with high concentrations of nitrogen compounds deleterious to nitrogen-sensitive reforming catalysts may be treated to obtain a substantially nitrogen-free product by contacting such contaminated hydrocarbon mixtures under denitrogenation conditions at elevated temperature and pressure in the presence of a hydrogen-affording gas and .a catalyst comprising a metal from Group VII-B of the Periodic Table supported on a porous solid cracking component.

Denitrogenation with a catalyst system such as dis- "ice closed and described herein offers several advantages when compared with processes of the prior art. Hydrocarbon mixtures originally containing high concentrations of nitrogen contaminants can be treated according to the present invention with effective lowering of nitrogen concentration levels at relatively high space velocities. The possibility of operating at high space velocities is important because space velocity is inversely proportional to volume of catalyst required, and, therefore, where it is possible to use high space velocities smaller volumes of catalysts will be required. By way of illustration, a hydrocarbon feed stock contaminated with 480 parts per million nitrogen was den-itrogenated over catalysts as listed in Table 1. Product nitrogen concentrations reported there illustrate that a substantially nitrogen-free product was obtained with the rhenium catalysts at a space velocity of 1.84. Even when space velocity was doubled to 3.68, these catalysts maintained their effectiveness, and a substantially nitrogenfree product was obtained. This is in contrast to the performance of the commercially available reference catalyst. At a space velocity of 1.84, product nitrogen concentration using the reference catalyst was 7 parts per million; when space velocity was increased by a factor of 2 to 3.68, product nitrogen concentration using the reference catalyst increased by a factor of 10. These data indicate that the rhenium catalysts are at least as effective at the higher space velocity as the reference catalyst is at the lower space velocity. This makes use of the rhenium catalysts especially attractive for denitrogenation because of their demonstrated effectiveness at relatively high space velocities.

TABLE 1 Product Nitrogen Concentration p.p.1n.

Catalyst 1. 84 3. 68

WI-ISV WHSV Reference 2 5.0 Wt. percent Re on Silica-Alumina 7.7 wt. percent Re on Silica-Alumina 3 1 Nitrogen analyses made by Kjeldahl Method accurate to i 3 ppm. 132113131; percent nickel and 19 wt. percent tungsten sulfides on silicaa 3 Average result of two runs made at; same conditions:

An object of this invention is a process for the purification of contaminated hydrocarbon mixtures. A further object of this invention is a process for the purification of contaminated hydrocarbon mixtures by contacting such contaminated hydrocarbon mixtures under denitrogenation conditions at elevated temperature and pressure and in the presence of a hydrogen-aifording gas with a catalyst comprising a minor amount of a metal from Group VIIB of the Periodic Table deposited upon a porous solid cracking base. A still further object of this invention is a process for the catalytic conversion under hydrocracking conditions of a higher boiling hydrocarbon mixture which originally was contaminated by nitrogen-containing compounds and which was subjected prior to said catalytic conversion to denitrogenation under denitrogenation conditions at elevated temperature and pressure in the presence of a hydrogen-affording gas and a catalyst comprising a minor amount of a metal from Group VII-B of the Periodic Table supported on porous solid cracking base.

In a preferred embodiment of the invention the denitrogenation process is carried out by contacting a heavy catalytically cracked cycle oil contaminated with a high concentration of nitrogen containing compounds boiling between about 300 F. and 850 F. in the presence of hydrogen at a temperature between about 600 F. and

about 900 F, a pressure between about 200 p.s.i.g. and about 5000 p.s.i.g., and a weight hourly space velocity between about 0.2 and 5 with a catalyst comprising: rhenium and a solid acidic cracking base, such as silicaalumina, to obtain a substantially nitrogen-free product.

The product of such a denitrogenation process can then be hydrocracked under hydrocracking conditions at elevated temperature and pressure in the presence of a hydrogen-affording gas with a suitable hydrocracking catalyst to form a lower boiling hydrocarbon mixture product.

In the operation of the process, a selected feed stock is contacted in a reaction zone containing catalyst along with a hydrogen containing gas such as hydrogen gas, catalytic reformer make-gas or a recycled hydrogen-rich gas from the present process. The process may be operated in the liquid phase, the vapor phase or mixed vapor-liquid phase. The catalyst system may be of the fixed bed type, as well as a fluidized bed or other appropriate type of system. The feed stocks employed may be derived from petroleum, shale, gilsonite or other such sources. Also it may be desirable to recycle a portion of the effluent to the reaction zone.

Nitrogen contaminated hydrocarbon feed stocks which may be satisfactorily denitrogenated according to the present invention may contain high concentrations of nitrogen-containing compounds. Most generally the original concentration of nitrogen-containing compounds in the contaminated hydrocarbon mixture feed stock will contain from about 20 to about 5000 parts per million nitrogen or higher. Advantageously, the original concentration of nitrogen-containing compounds Will be in the range from about 200 to about 1200 parts per million nitrogen. Contaminated hydrocarbon mixtures which may be satisfactorily denitrogenated in the present process may have compositions ranging from essentially all saturates to all aromatics. High boiling fractions of crude oil constitute advantageous feed stocks for the process of the invention. Most generally the feed stock will range from naphtha and kerosene through the light and heavy gas oils. The feed stock will normally boil above about 300 F. and may boil up to about 1000 F. Advantageously, the boiling range of the feed stock is about 300 F. to about 850 F. Examples of desirable feed stocks are nitrogen-contaminated light catalytic cycle oil having a boiling range of from about 350 F. to about 650 F., heavy catalytic cycle oil boiling in the range of about 500 F. to about 850 F., virgin gas oil boiling from about 400 F. to about 1000 F. and coker gas oil boiling in the range of about 350 F. to about 800 F.

The process conditions which are employed in the present invention can be selected over a relatively wide range and are correlated, according to the nature of the feed stock and of the particular catalyst employed, so as to produce a substantially nitrogen-free product. Satisfactory denitrogenation is obtained with the abovedescribed feed stocks under denitrogenation conditions which include pressures in the range of about 200 to about 5000 p.s.i.g. and temperatures in the range of about 600 to about 900 F., although pressures and temperatures outside of these ranges may be employed when utilizing certain feed stocks. Advantageously, pressures in the range of about 500 to about 1500 p.s.i.g. and temperatures between about 650 and about 750 F. are employed. It may be desirable during the course of a run to increase the temperature Within the reaction zone as the catalyst deactivates in order to compensate for a drop in catalyst activity.

The space velocity, expressed herein as weight hourly space velocity (WHSV), may range from about 0.1 to about 10, normally from about 0.2 to about 5, and preferably from about 1.5 to about 4.

Hydrogen is consumed in the process and it is neces sary to maintain an excess of hydrogen in the reaction zone. However, the process is relatively unaffected by changes in the hydrogen to oil ratio within the general range of operations. The hydrogen to oil ratio employed desirably is in the range of about 1000 to 20,000 standard cubic feet of hydrogen gas per barrel of feed (s.c.f.b.) and advantageously about 6,000 to about 14,000 standard cubic feet of hydrogen per barrel of feed is employed.

Typically, the active metal component of the catalyst is carried on a porous solid support. Such support may comprise one of the type commonly found in the art having a high porosity and a surface area on the order of about to about 500 square meters per gram. Preferred as catalyst supports are one or more of the acidic catalyst supports such as silica-alumina (naturally occurring and/or synthetic) silica-magnesia, silica-alumina-zirconia, and the like. Other acidic catalyst supports contemplated for use in the practice of this invention include acid-treated-aluminas, with or without halogens, such as fluorided alumina, boria-alumina, and the hoteropoly-acid-treated aluminas, i.e., treated with phosphotungstic acid, phosphovanadic acid, silicotungstic acid, silicomolybdovanadic acid and the like, may be employed. In one specific embodiment the preferred acidic component is a commencially available synthetic silica-alumina cracking catalyst containing about 5 to about 40 weight percent alumina. The preparation and properties of the support components are well-known in the art and they need not be described further herein for the purpose of the present invention. For example, see the series entitled Catalysis by Emmett (Reinhold Publishing Corporation), particularly Volume VII, pp. 191.

It is critical that a minor amount of a metal from Group VII-B of the Periodic Table, be deposited upon the porous solid acidic base. The Group VII-B metal can be used either alone or in combination with one or more of the Group VI, and Group VIII hydrogenation metals. The Group VII-B metallic component can be incorporated into the catalyst by impregnating a porous acidic component with a decomposable compound of the active metal, followed by drying and calcining to provide a composite. Typically, a silica-alumina cracking catalyst is impregnated with a solution containing rhenium heptoxide and 30 percent aqueous ammonia, and then dried to a powder; followed by pelleting and calcining for about 4 hours at an elevated temperature in the range of about 600 to about 800 F. Another illustrative method of catalyst preparation consisting of impregnating a silicaalumina cracking catalyst with a solution of ammonium perrhenate followed by drying, pelleting and calcining for about 4 hours at an elevated temperature in the range of about 600 to about 800 F. The finished catalyst is then pre-sulfided by treating with a hydrogen sulfide/hydrogen mixture typically containing about 8 percent hydrogen sulfide.

However, it is contemplated that the finished catalyst may also be produced by various other methods and techniques, such as vapor deposition of decomposable organic compounds containing the active Group VII-B metal with subsequent evaporation of the solvent followed by drying and calcining.

The amount of the Group VII-B metal incorporated in the catalyst can vary over a wide range, with the amount being selected to provide the desired catalyst activity. For example, large amounts of rhenium, up to about 30 percent by weight, can be employed, and relatively small amounts of rhenium, as little as 0.5 percent by weight, also are effective with about 1 to about 10 percent by weight being preferred.

After a period of operation wherein the catalyst is contacted with a contaminated hydrocarbon feed, the catalyst activity may decline, with carbonaceous deposits being accumulated on the catalyst. When the catalyst activity declines to a point where the catalyst is not suitable for further use, the catalyst can be regenerated to restore its activity and enable the hydrocarbon conversion to be attained.

A nitrogen containing contaminated hydrocarbon mixture which has been treated as described herein to produce a substantially nitrogen-free product may be further processed to form a lower boiling hydrocarbon mixture by catalytic conversion under hydrocracking conditions at elevated temperature and pressure in the presence of a hydrogen-alfording gas and a hydrocracking catalyst. Hydrocracking catalysts suitable for use in the catalyst conversion of denitrogenation hydrocarbon feed stocks can be nitrogen-sensitive and may include those catalysts known to the art. Typically, metallic hydrogenation components selected from Group VI and Group VIII of the Periodic Table either alone or in mixtures thereof, may be used either in elemental form or as oxides and sulfides thereof and are supported upon a porous solid acidic cracking base having substantially cracking activity in a finished catalyst composition such as silica-alumina (naturally occurring and/or synthetic) silica-magnesia, and the like. Elements which have been found capable of providing an advantageous balance in activities between the metallic hydrogenation component and the porous solid acidic component may be included in the hydrocracking catalyst composition. These elements include the normally solid elements of Group VI-A of the Periodic Table especially sulfur; the normally solid elements of Group VA of the Periodic Table, especially arsenic and antimony; and certain metals such as silver, lead, mercury, copper, zinc, and cadmium, although the elfectiveness of each is not necessarily the same.

Hydrocracking conditions for such a process may include pressures in the range of about 200 to about 2000 p.s.i.g, and temperatures in the range of about 400 to about 1000 F. although pressures and temperatures outside of these ranges may be employed when utilizing certain feed stocks. Advantageously, pressures in the range of about 750 to 1500 p.s.i.g and temperatures between about 500 and 700 F. are employed. Space velocities of such hydrocracking catalyst may range from about 0.1 to about 10 liquid hourly space velocity (LHSV), normally from about 0.2 to 5, and preferably from about 0.25 to 2. Lower space velocities tend to increase the degree of conversion.

Hydrogen is consumed in such a hydrocracking process, and it is necessary to maintain an excess of hydrogen in the reaction zone. However, the process is relatively unaffected by changes in the hydrogen to oil ratio within the general range of operations. The hydrogen to oil ratio employed desirably is in the range of about 1000 to 20,000 standard cubic feet of hydrogen gas per barrel of feed (s.c.f.b.) and advantageously about 2500 to 10,000 s.c.f.b. is employed.

The following example is given by way of illustrating the practice of this invention. A catalyst prepared according to the methods described in this specification containing weight percent rhenium on a support comprising a synthetic silica-alumina cracking containing about 25 weight percent alumina is pre-sulfided for 1 hour at 720 F. and atmospheric pressure in the presence of an 8 percent hydrogen sulfide/hydrogen mixture. The finished catalyst is contacted with a heavy catalytically cracked cycle oil having an API gravity of 21 containing 480 parts per million nitrogen in a reactor for pre-treatment to lower the level of nitrogen contaminants. Conditions in the first reaction zone include a temperature of 720 F., a pressure of 1000 p.s.i.g., and the presence of 10,000 standard cubic feet of hydrogen per barrel of oil. Weight hourly space velocity (WHSV) is 2. Effluent from the first reaction zone is found to contain about 1 part per million nitrogen. The pre-treated heavy catalytically cracked cycle oil is then sent to the second reactor for hydrocracking. The second reactor contains a catalyst prepared by adding 400 cubic centimeters of a solution consisting of 45 grams of nickel acetate tetrahydrate in distilled water to 200 grams of a synthetic silica-alumina cracking catalyst containing 25 weight percent alumina and having been dried at 400 F. for 1 hour. The catalyst is soaked with stirring for 1 hour, then dried at 400 F. and calcined at 1000 F. for 4 hours. The finished 'hydro cracking catalyst contains 5 .3 weight percent nickel. The pro-treated heavy catalytically cracked cycle oil from the first reactor is then contacted in the second reactor with the finished hydrocracking catalyst under the following conditions: temperature of 610 F., pressure of 1000 p.s.i.g liquid hourly space velocity (LHSV) of 1.5, and a hydrogen to oil ratio of 7000 standard cubic feet per barrel. The reactor effluent is analyzed and found to contain about 70 percent by weight of a product boiling in the gasoline range.

The following examples are given for the purpose of illustrating the practice of the present invention. However, it is to be understood that these examples are given by way of exemplification only and do not serve in any way to limit the scope of the present invention.

Example 1 6.50 grams of rhenium heptoxide were dissolved in 25 milliliters of water, and 10 milliliters of 30 percent aqueous ammonia was added. The mixture was diluted to milliliters and gently heated to dissolve any percipitated ammonium perrhenate. A synthetic silicaalumina cracking catalyst containing about 25 weight percent alumina was impregnated with this aqueous solution. The mixture was dried to powder, pelleted, and calcined for 4 hours at 740 F. The catalyst was then pre-treated for 1 hour at 720 F. and atmospheric pressure in the presence of an 8 percent hydrogen sulfide/hydrogen mixture. The finished catalyst containing about 5 weight percent rhenium was contacted with a heavy catalytically cracked cycle oil having an API gravity of 20.7 and 480 parts per million nitrogen in a reactor at a temperature of about 720 F., a pressure of about 1000 p.s.i.g., and in the presence of about 10,000 standard cubic feet of hydrogen per barrel of oil. Weight hourly space velocity (WHSV) was 1.84. The reactor efiluent was analyzed and found to contain 0 parts per million nitrogen. A second test was performed under conditions identical to those related above with the exception that weight hourly space velocity (WHSV) was doubled to 3.68. The reactor effluent was again analyzed and found to contain 5 parts per million nitrogen.

Example 2 A denitrogenation catalyst was prepared according to the method described in Example 1 except that 10.0 grams of rhenium heptoxide were used, and the finished catalyst was analyzed to contain about 7.7 weight percent rhenium. The finished catalyst was contacted with a feed stock containing 480 parts per million nitrogen substantially as described in Example 1. The reactor eflluent was analyzed and found to contain 1 part per million nitrogen when a space velocity of 1.84 was employed. When the space velocity was doubled to 3.68, the reactor effluent was analyzed to contain 1 part per million nitrogen.

Example 3 A catalyst was prepared and pre-treated according to the method described in Example 1 except that 1.30 grams rhenium heptoxide were used, and the finished catalyst was analyzed to contain about 1 weight percent rhenium. This catalyst was then contacted with a feed containing substantially 480 parts per million, as described in Example 1 and found to contain 3 parts per million nitrogen when a weight hourly space velocity (WHSV) of 1.84 was employed. When the space velocity was doubled to 3.68, the reactor efiluent was analyzed and found to contain 35 parts per million nitrogen.

From the foregoing examples it is apparent that the process employing the catalyst described in the examples is capable of denitrogenating hydrocarbon mixtures contaminated with high concentrations of nitrogen-containing compounds to produce a substantially nitrogen-free product.

From the foregoing description of the present invention modifications and variations in the operation of the process will become apparent to the skilled artisan and as such, fall within the scope and spirit of the present invention.

I claim:

1. A process for the denitrogenation of nitrogen-contaminated hydrocarbon mixtures which process comprises contacting said hydrocarbon mixtures under denitrogenation conditions in the presence of a hydrogen-affording gas and a catalyst comprising a rhenium denitrogenation component on a porous solid acidic cracking catalyst base to produce a substantially nitrogen-free product.

2. The process of claim 1 wherein rhenium is present in an amount from about 0.5 to about 30 percent by weight and where said porous solid acidic catalyst base is silicia-alumina.

3. The process of claim 1 wherein said hydrocarbon mixture is heavy catalytically cracked cycle oil boiling in the range of about 500 F. to about 850 F.

4. The process of claim 3 wherein said denitrogenation conditions include a temperature between about 600 F. and about 900 F., a pressure between about 200 and 5000 p.s.i.g. or higher, and a weight hourly space velocity between about 0.1 and about 10.

5. A process for the denitrogenation of petroleum distillates which comprises contacting a heavy catalytically cracked cycle oil boiling from about 500 F. to about 850 F. in the presence of a catalyst comprising from about 1.0 to about 10.0 weight percent rhenium on a silicia-alumina support at a temperature from about 650 F. to about 750 F., a pressure from about 500 to about 1500 p.s.i.g., and a weight hourly space velocity from about 0.2 to about 5.0 to produce a substantially nitrogen free product.

6. The process of claim 1 wherein said nitrogen-contaminated hydrocarbon mixtures contain from about 20 to about 1200 parts per million nitrogen.

References Cited by the Examiner UNITED STATES PATENTS 2,894,898 7/ 1959 Oettinger et al 208213 3,008,895 11/1961 Hansford et al 208-89 3,055,823 9/1962 Mason et al. 208-254 DELBERT E. GANTZ, Primary Examiner.

PAUL M. COUGHLAN, ALPHONSO D. SULLIVAN,

Examiners. 

1. A PROCESS FOR THE DENITROGENATION OF NITROGEN-CONTAMINIATED HYDROCARBON MIXTURES WHICH PROCESS COMPRISES CONTACTING SAID HYDROCARBON MIXTURES UNDER DENITROGENATION CONDITIONS IN THE PRESENCE OF A HYDROGEN-AFFORDING GAS AND A CATALYST COMPRISING A RHENIUM DENITROGENATION COMPONENT ON A POROUS SOLID ACIDIC CRACKING CATALYST BASE TO PRODUCE A SUBSTANTIALLY NITROGEN-FREE PRODUCT. 